1. Field of the Invention
The invention relates generally to arc lamps and specifically to lamps with short arcs capable of operating at two kilowatts.
2. Description of the Prior Art
Short arc lamps provide intense point sources of light that allow light collection in reflectors for applications in medical endoscopes, instrumentation and projection. Short arc lamps are used in industrial endoscopes for the inspection of jet engine interiors.
A typical short arc lamp comprises an anode and a cathode positioned along the longitudinal axis of a cylindrical, sealed concave chamber that contains a gas pressurized to several atmospheres. U.S. Pat. No. 4,633,128, issued Dec. 30, 1986, to Roy D. Roberts, the present inventor, and Robert L, Minor, describes such a short arc lamp in which a copper sleeve member is attached to the reflecting wall to conduct heat from the reflecting wall through to the exterior wall and eventually to circulating ambient air.
The lamp illustrated in FIG. 2 of Roberts, et at., can be operated at one kilowatt. At higher power levels, the heat generated by an electric arc between cathode 94 and anode 100 encounters too much thermal resistance to the ambient and the lamp can overheat and fail. Specifically, applying too much power to the lamp creates thermal gradients in the ceramic material that will cause cracks in the body and possibly an explosion of a weakened lamp.
FIG. 1 illustrates a prior art short arc lamp 10. The lamp 10 comprises a cathode 12, a cathode suspension strut 13, an anode 14, a reflecting concave wall 16 in a ceramic alumina body 18, a window 20, metallic base 22, a first metal band 24, a second metal band 26 and a copper heat-transfer pad 28. In operation, an electric arc 30 bridges the gap between cathode 12 and anode 14. Base 22 is typically comprised of iron and functions to electrically connect anode 14 to first metal band 24. Heat generated by electric arc 30 is conducted away by passing through body 18, especially wall 16 near anode 14 to copper heat-transfer pad 28 and again through body 18 to first metal band 24. An air fin heat sink, not shown, slips over and tightly around first metal band 24 to provide heat sinking to circulating forced air. A second heat path is through anode 14 and rear of base 22 and to first metal band 24.
A more efficient transfer of heat is therefore needed to operate short arc lamps at power levels of two kilowatts.